Influence of Petrographic, Geochemical, and Pore-Associated Matrix Characteristics on CH and CO Sorption of Coal and Shale from Early Permian-Gondwana Deposits, India.

CO storage in various geological formations presents a feasible option for reducing greenhouse gas emissions (GHG) in the atmosphere. The most viable and technoeconomic method involves injecting CO into deep, unmineable coal seams and shale beds to enhance CH recovery. CO exhibits a greater affinity with coal, shale, and associated siliciclastic-organic rich rock compared to CH. However, detailed information about the coal and shale reservoirs is crucial prior to the CO injection and enhanced CH recovery. This study aims to evaluate the petrographic, geochemical (proximate, ultimate), and pore-matrix characteristics of coal and shale samples to assess the enhanced CH recovery through CO injection. Pore distribution studies, conducted through micropetrography, Field Emission Scanning Electron Microscopy photographs, and low-pressure BET sorption isotherms, categorized the pore structures of coal and shale into three types: cylindrical, slit, and wedge-shaped. These pore structures, particularly the end-opening of the pores, were found to be suitable for gas storage and release. Clays intermixed with organic matter formed pores, which created suitable adsorption sites for CH and CO. The studied coal exhibited higher CH diffusivity and gas saturation compared to shale, favoring CH recovery with CO injection. The dominating collotelinite maceral has a positive relation with the Langmuir volume ( ) of CH and CO favoring greater sorption in coal/shale. Conversely, the semifusinite and sporinite macerals influence gas accumulation and diffusivity. The CH diffusivity of coal seam ranges from 2.355 × 10 to 4.019 × 10 min (avg. 3.197 × 10 min), while shale diffusivity ranges from 1.185 × 10 to 2.371 × 10 min (avg. 1.531 × 10 min). The higher diffusivity in coal is supported by the pore distribution and cleat intensity. The sorption ratio of CH and CO, which is directly proportional to in situ gas, indicates an increase in CH diffusion and CO adsorption. Increasing vitrinite reflectance (VR) values indicate improved maturity of coal and shale, associated with changes in macromolecular structures and pore-matrix systems suitable for CO storage.